Electric circuit breaker with electromagnetically assisted closing means

ABSTRACT

Discloses an electric circuit breaker that includes electromagnetic assist means for opposing the magnetic contactrepulsion forces developed when a high current flows through the circuit breaker. The electromagnetic assist means comprises flexible conductive means in series with the contacts of the breaker for carrying the inter-contact current through a loopshaped path where a magnetic closing force is developed on the contacts. Only a minor portion of the total inter-contact current is conducted through the loop-shaped path. For carrying the remaining and major portion of the current, additional flexible conductive means is connected in series with the contacts and in parallel with the loop-shaped path, and this additional conductive means follows a path separate from and independent of the loop-shaped path. Sufficient closing force is obtained from the minor portion of the total current that passes through the loop-shaped path to hold the contacts engaged during the highest current surges for which the breaker is rated.

United States Patent Klint I Q [151 3,665,350 [451 May 23, 1972 [541'ELECTRIC CIRCUIT BREAKER WITH ELECTROMAGNETICALLY ASSISTED c osmc MEANSPrimary Examiner-Harold Broome Attorney-J. Welsey Haubner and WilliamFreedman [57] ABSTRACT Discloses an electric circuit breaker thatincludes electromagnetic assist means for opposing the magneticcontact-repulsion forces developed when a high current flows through thecircuit breaker. The electromagnetic assist means comprises flexibleconductive means in series with the contacts of the breaker for carryingthe inter-contact current through a loopshaped path where a magneticclosing force is developed on the contacts. Only a minor portion of thetotal inter-contact current is conducted through the loop-shaped path.For carrying the remaining and major portion of the current, additionalflexible conductive means is connected in series with the contacts andin parallel with the loop-shaped path, and this additional conductiveme'ans follows a path separate from and independent of the loop-shapedpath. Sufiicient closing force is obtained from the minor portion of thetotal current that passes through the loop-shaped path to hold thecontacts engaged during the highest current surges for which the breakeris rated.

4 Claims, 2 Drawing Figures l6 a" Md 0 a l 26 100 20/ l u u I 204 74 u nF .r 7r 3 70 a: 50 V J4 44 as 42 Q 40 [ff-m 42a Patented May 23, 19723,665,350

INVENTOR. ROBERT 1 AL/NT,

r J e A TTORIVE) v 1 ELECTRIC CIRCUIT BREAKER WITH ELECTROMAGNETICALLYASSISTED CLOSING MEANS.

CROSS-REFERENCE TO RELATED APPLICATION -This application is related toapplication Ser. No. 865,046- Barkan et al., filed Oct. 9, 1969 andassigned to the assignee of the present invention, which application isincorporated by reference in the present application.

BACKGROUND This invention relates to an electric circuit breaker thatineludes electromagnetic means for opposing the magneticcontact-repulsion forces developed when a high current flows through thecircuit breaker. This type of circuit breaker is referred to hereinafteras a circuit breakerwith electromagnetically-assisted closing means.

A circuit breaker with electromagnetically assisted closing means isdisclosed and claimed in the aforesaid Barkan et al application, and thepresent-application discloses and claims an improvement thereof. Thecircuit breaker of the Barkan et al., application comprises a firstcontact and a second contact movable into engagement with said firstcontact to close the circuit breaker and movable out of engagement withsaid first contact to open the circuit breaker. The electromagneticassist means develops a magnetic closing force on the movable contactwhich varies directly in accordance with the current throughthecontacts. This assist means comprises conductive means in series withsaid contacts for carrying the intercontact current through aloop-shaped path that comprises a pair of series-connected anns betweenwhich a repulsive magnetic DETAILED DESCRIPTION OF PREFERRED EMBODIMENTThe circuit breaker shown in FIG. 1 is in many respects similar to thatshown and claimed in the aforesaid Barkan et al application.Accordingly, the same reference numerals are used for the parts of FIG.1 as are used for corresponding parts in the Barkan et al application;and reference may be had to said Barkan et al application for a detaileddescription of such parts. Generally speaking, where the parts have beenfully described in the Barkan et al., application, they will not besatisfactory for circuit breakers of low and moderate current SUMMARY Anobject of the present invention is to provide a high current circuitbreaker with electromagnetically assistedclosing means in which thevolume of the braid in the loop region is limited to a relatively lowvalue despite the high current rating of the circuit breaker.

In carrying out the invention in one form, I conduct only a minor partof the total current that passes through the contacts through theloop-shaped path. For carrying the remaining and major portion of thecurrent, additional braid is connected in series with the contacts andin parallel with the loop- I shaped path, and this additional braidfollows a path separate from and independent of the loop-shaped path.Sufficient closing force is'obtained from the minor portion of the totalcurrent that passes through the loop-shaped path to hold the contacts inengagement during the highest current surges for which the circuitbreaker is rated.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a side elevational view of acircuit breaker embodying one form of the invention, the circuit breakerbeing.

shown in its fully closed position.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

described in the present application except insofar as necessary toprovide an understanding of the present invention. Emphasis in thepresent description will be placed on those features that are not shownin the Barkan et al application.

In the circuit breaker of FIG. 1 the electromagnetic-assist means 60comprises a flexible conductor 62 of a loop-shaped form connected inseries with contacts ll, 12. One end of the flexible conductor 62 issuitably connected to contact rod 17 at 63, and the opposite end isconnected at 64 to a terminal stud 65, preferably of copper. Flexibleconductor 62 is preferably of copper braid and may be thought of ascompris ing two series-connected arms 67 and 68. The arm 67 and stud 65are fixed to a stationary supporting frame 70. This supporting frame 70is preferably of a low conductivity metal so that no appreciable part ofthe current flows therethrough. Most of the braid 62 is physicallyconnected to other parts of the electromagnetic assist means 60, as willsoon be explained.

The electromagnetic-assist means 60 further comprises a togglecomprising two toggle links 74 and 75 pivotally joined together at aknee 76. Upper toggle link 74 has its upper end pivotally connected tocontact rod 17 by a pivot pin 77. Lower toggle link 75 has its lower endpivotally mounted at 78 on a toggle support lever 80. Toggle supportlever 80 has one end pivotally mounted on a fixed pivot 82 carried byframe 70. The opposite, or free, end of toggle support lever 80 isrestrained in its position of FIG. 1 by a releasable latch 83 thatcooperates with a latch roller 85 carried by lever 80. A suitable stop86 prevents counterclockwise motion of lever 80 past its position ofFIG. 1. The latch 83 is pivoted on a stationary pivot 87 carried byframe 70.

Returning now to the flexible conductor 62, the lower portion of thisconductor is mechanically connected to the toggle support lever 80, andthe arm 68 is mechanically-connected to the two toggle links 74 and 75.Current flowing at any given instant through the loop-shaped conductor62 passes in opposite' directions through the two arms 67 and 68,developing magnetic fields around the two arms that interact in a knownmanner to produce a repulsive magnetic force F that urges the armsapart. This repulsive magnetic force varies directly with the square ofthe current passing through the loop-shaped conductor. The effect ofthis repulsive magnetic force is to urge the toggle 74, 75 toward anin-line or extended position, thus developing a force on the contact rod17 that acts in an upward closing direction. The geometry of the toggle74, 75 is preferably such that the electromagnetic repulsion forcebetween the .two arms 67 and 68 is multiplied by a factor of 2 or 3.Thus, when high currents flow through contacts l1, 12 to produce acontact separating force, a larger than proportional closing force isdeveloped by the magnetic-assist means 60 to oppose thecontact-separating force. Toggle linkage 74, 75 is a highly eflicientarrangement for producing this desirable force-multiplying effect.

In the circuit breaker of the Barkan et al., application which uses thebraid 62, all the current that passes through the contacts also passesthrough braid 62. As pointed out hereinabove, this is satisfactory forcircuit-breakers of low or moderate current ratings, but it has aserious disadvantage for high current ratings,- e. g., those with asteady state current rating of 2,000 amperes or greater. Thisdisadvantage is that the volume of the braid required to carry the highcurrent is too great to permit a reasonable size loop to be formed in aloopshaped path.

I overcome this problem by using the loop-shaped braid 62 for carryingonly a minor portion of the current through the contacts. For carryingthe major portion of the current, I provide additional segments offlexible braid 200 and 201 in series with the contacts 11, 12 and inparallel with the loopshaped braid 62. This additionalbraid 200 and 201extends between the stud 65 and the movable contact rod 17 via a pathwhich is separate andindependentfrom the loop-shaped path followed bybraid 62. Current flowing through additional braid 200, 201 develops noclosing force on the movable contact rod 17. It is to be understood thatthe flexibility of the braid segments 200 and 201 allows contact rod 17to move between open and closed positions with no substantial restraintfrom these braids.

The braid segment 201 is electrically connected at its right hand end toa stud 204, which in turn is electrically connected to the stud 65 by aconductor 206 which extends around a portion of frame 70 externallythereof. This relationship can be seen in FIG. 2.

For properly distributing the current through the various braids 200,201 and 62, I match the impedances of these braids so that only a minorportion (i.e., less than half) of the total current flows through braid62. The remaining and major portion of the total current is dividedbetween the braids 200 and 201.

Because only a minor portion of the total current flows through theloopshaped braided conductor 62, the cross sectiorlal area of thisconductor 62 can be kept relatively small; and the loop therein cantherefore be made relatively sharp and can thus be accommodated in arelatively small space.

Although only a minor portion of the total current flows through theloop-shaped conductor 62, sufiicient closing force is developed therebyon movable contact rod 17 to hold the contacts ll, 12 in engagementagainst the highest current surges that the circuit breaker is rated tocarry. It is to be understood, of course, that this closing force isdeveloped only when the toggle support lever 80 is restrained in itsposition of FIG. 1 by latch 83. Current through the other braids 200 and201 develops no significant closing force on contact rod 17.

Although in a preferred form of my invention, a major portion (i.e.,greater than 50 percent) of the total current is carried by the braids200 and 201, it is to be understood that my invention in its broaderaspects comprehends an arrangement in which a somewhat smaller percentof the total current is through these braids 200 and 201. In any case,however, an appreciable portion, i.e., greater than one-third of thetotal current, should be carried by means (200, 201) paralleling theloop-shaped conductor 62 of the magnetic assist means 60.

Suitable local insulation such as shown at 211 is preferably provided toconfine the current to the braids 68, 200, and 201 and thus to minimizethe passage of current through frame 70.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschangesand modifications maybe made without departing from my inventionin its broader aspects; and I, therefore, intend herein to cover allsuch changes and modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: l

1. An electric circuit breaker comprising:

a. a first contact,

b. a second'contact movable into engagement with said first contact toclose said circuit breaker and movable out of between which a repulsivemagnetic force is developed that urges said arms apart when currenttraverses said loop-shaped path, and means for converting said repulsiveforce into said magnetic closing force on said movable contact,

e. andadditional conductive means in series with said contacts and inparallel with said first conductive means for carrying another portionof the intercontact current to and from said movable contact via a paththat is spaced from and independent of said loop-shaped path, saidadditional conductive means carrying at least one-third of the totalcurrent through said circuit breaker.

The circuit breaker of claim 1 in which:

a. said first conductive means comprises first flexible conductive braidin a region where said series connected arms are joined for permittingrelative movability of said arms,

. said additional conductive means comprising additional flexibleconductive braid that is spaced from said first braid,

c. said additional braid being capable of flexing in response tomovement of said movable contact and arranged so that current flowingtherethrough develops no substantial closing force on said movablecontact.

3. The circuit breaker of claim 1 in which said first conductive meanscarries a minor portion of the intercontact current and said additionalconductive means carries a major portion of the intercontact current.

4. The circuit breaker of claim 1 in which said additional conductivemeans is constructed and arranged so that current flowing therethroughdevelops no substantial closing force on said movable contact.

1. An electric circuit breaker comprising: a. a first contact, b. asecond contact movable into engagement with said first contact to closesaid circuit breaker and movable out of engagement with said firstcontact to open the circuit breaker and the circuit therethrough, c.electromagnetic assist means for developing a magnetic closing force onsaid movable contact which varies directly in accordance with currentthrough said contacts, d. said electromagnetic assist means comprisingfirst conductive means in series with said contacts for carrying aportion of the intercontact current through a loop-shaped path thatcomprises a pair of series-connected arms between which a repulsivemagnetic force is developed that urges said arms apart when currenttraverses said loop-shaped path, and means for converting said repulsiveforce into said magnetic closing force on said movable contact, e. andadditional conductive means in series with said contacts and in parallelwith said first conductive means for carrying another portion of theintercontact current to and from said movable contact via a path that isspaced from and independent of said loop-shaped path, said additionalconductive means carrying at least one-third of the total currentthrough said circuit breaker.
 2. The circuit breaker of claim 1 inwhich: a. said first conductive means comprises first flexibleconductive braid in a region where said series connected arms are joinedfor permitting relative movability of said arms, b. said additionalconductive means comprising additional flexible conductive braid that isspaced from said first braid, c. said additional braid being capable offlexing in response to movement of said movable contact and arranged sothat current flowing therethrough develops no substantial closing forceon said movable contact.
 3. The circuit breaker of claim 1 in which saidfirst conductive means carries a minor portion of the intercontactcurrent and said additional conductive means carries a major portion ofthe intercontact current.
 4. The circuit breaker of claim 1 in whichsaid additional conductive means is constructed and arranged so thatcurrent flowing therethrough develops no substantial closing force onsaid movable contact.